System and method for fast dynamic link adaptation

ABSTRACT

A method and user equipment for selecting a transport format combination (TFC) is disclosed. Configuration of a plurality of TFCs to use for TFC selection is received, wherein the TFCs of the plurality of TFCs have an order. TFCs to block from TFC selection from the plurality of TFCs is determined, wherein the TFCs to block are based at least on a maximum allowed transmit power. A TFC for transmission of uplink data is selected, wherein the selected TFC is based on the TFC order and wherein the selected TFC is a TFC that is not blocked from TFC selection.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/035,125, filed Feb. 25, 2011, which is a continuation of U.S. patentapplication Ser. No. 11/959,578, filed Dec. 19, 2007, which issued asU.S. Pat. No. 7,903,616 on Mar. 8, 2011, which is a continuation of U.S.patent application Ser. No. 11/503,822, filed Aug. 14, 2006, whichissued as U.S. Pat. No. 7,313,117 on Dec. 25, 2007, which is acontinuation of U.S. patent application Ser. No. 11/007,955, filed Dec.9, 2004, which issued as U.S. Pat. No. 7,092,371 on Aug. 15, 2006, whichis a continuation of U.S. patent application Ser. No. 10/273,302 filedOct. 17, 2002, which issued as U.S. Pat. No. 6,845,088 on Jan. 18, 2005,which claims the benefit of U.S. Provisional Application No. 60/344,693filed on Oct. 19, 2001, all of which are incorporated by reference as iffully set forth.

FIELD OF INVENTION

The present invention is related to the field of wirelesscommunications. More particularly, the invention is directed to a systemand method for fast dynamic link adaption in third generation wirelesscommunication systems.

BACKGROUND

In Third Generation (3G) communication systems, Dynamic Link Adaptation(DLA) is used to compensate for degraded radio propagation conditionsthat would require the User Equipment (UE) to transmit at a transmissionpower greater then the maximum allowed, or physical maximum,transmission power. Transmissions that require to be transmitted at apower level greater than the maximum power level are transmitted at themaximum power level in 3G communication systems. When these signals aretransmitted at the maximum power level (which is less than their desiredtransmit power level) they experience degraded performance and haveincreased error rates, increasing the likelihood that the transmitteddata will not be received, and that the system resources being used arebeing wasted.

One prior art method for handling this maximum power condition is tocontinue the transmission at the maximum allowed or physical maximumtransmission power and rely on the error correction capabilities of thereceiver to correct any errors that may occur. This ultimately resultsin undesirable system performance, since the transmission will be madeat a power level that is not adequate to maintain the desired level oferror rate performance.

Another method for dealing with the maximum power condition is to reducethe Uplink (UL) data requirement for the period that the requiredtransmission power to maintain the desired level of error rateperformance is greater than the maximum power capability. This methodmaintains the desired error rate performance by the reduction of thedata rate.

It is also possible to continue UL transmissions when the desired powerwould exceed the maximum power capability without effecting the UL datarequirement by allowing the Block Error Rate (BLER) to increase. Thiseffect is considered to be unavoidable for the period from when themaximum power condition is perceived to when the UL transmissions can bereconfigured to a reduced overall rate. In 3G wireless standards, UEperformance requirements are specified that limit this period.

There is strong motivation to exceed the specified requirements sincetransmissions that require a power level greater than the maximumtransmit power level are likely to fail. Services that allow for dataretransmission of failed transmissions result in increased overhead,reduced radio resource efficiency and reduced UE battery life. Servicesthat do not allow for retransmission result in an increase in the BLER,thereby causing subsequent increased power requests to attempt tomaintain the BLER quality target. Since the UE is already transmittingat its maximum power, an increase in signal to interference ratio SIRtarget used in the UL transmit power control algorithm does not improvethe BLER performance for the current channel conditions. If the channelconditions improve, the increased SIR target will require the UE totransmit at a power level greater than necessary to maintain the desiredperformance, resulting in reduced radio resource efficiency and batterylife.

To achieve or exceed the performance requirements for improved Qualityof Service (QoS), an efficient method of adjusting the UL transmissionrequirements is necessary.

In 3G communication systems, individual data streams are assigned toTransport Channels (TrCHs) with specific QoS capabilities, which areconfigured to achieve specified BLER quality targets. The physicalchannel(s) assigned to the UE support multiple TrCHs simultaneously;this is called a Coded Composite Transport Channel (CCTrCH). The CCTrCHallows for varying amounts of data on each TrCH to exist in any specificTransmission Time Interval (TTI). The TTI period is specific to eachTrCH. Within each TTI period for a specific TrCH, the amount of datatransmitted is specified by a Transport Format (TF).

For the CCTrCH in any specific TTI period, the set of TFs for each TrCHis known as the Transport Format Combination (TFC). The set of all ofthe available TFCs, (i.e. all of the available allowed multiplexingoptions), is known as the Transport Format Combination Set (TFCS).

For each UL CCTrCH, the UE Medium Access Control (MAC) entity selects aTFC for transmission on a TTI basis. This TFC and associated data isprovided to the physical layer for transmission in the physical datarequest primitive. If the physical layer subsequently determinestransmission of this TFC exceeds the maximum or allowable UEtransmission power, a physical status indication primitive is generatedto the MAC to indicate that maximum power or allowable transmissionpower has been reached.

When the MAC is informed of the maximum or allowable transmission powerhas been reached, the TFCs that would cause this condition to continueto exist are blocked, that is, removed from the set of available TFCs,unless the TFC is one of the TFCs which according to the 3GPP standardscannot be blocked. Blocked TFCs may be later restored to the set ofavailable TFCs by unblocking them in subsequent periods when the UEtransmission power measurements indicate the ability to support theseTFCs with less than or equal to the maximum or allowed UE transmissionpower.

There are, however serious drawbacks with the current manner in whichTFCs are removed. As aforementioned, the physical layer determineswhether the transmission of a TFC would require exceeding the maximum orallowable UE transmission power, and then a physical status indicationprimitive is generated to the MAC entity that indicates maximum power orallowable power has been reached. Using this method, the UE could be inthe maximum power state for approximately 60 milliseconds or more whilethe MAC reconfigures the set of available TFCs to remove the blockedTFCs and start selecting TFCs from the updated set of available TFCs.The UE will reduce the available TFCs only to the power requirement forthe TFC that exceeded the transmission power capability. The UE willthen likely choose the TFC with the next lower transmission powerrequirement. However, there is no guarantee that the reduced set of TFCswill not require power in excess of the maximum power. This results inanother iteration of the process, and an additional delay, to furtherreduce the set of TFCs. For each TFC that is eliminated, data and radioresources are lost for the given TTIs. Ultimately, the performance ofthe system is degraded during the maximum power condition.

Additional performance concerns arise when the UE is attempting torecover the TFCs that have been blocked due to the maximum powercondition. It is desirable to unblock, (i.e., recover), TFCs as quicklyas possible to have a more complete set of TFCs available for the UE touse. Ultimately, the performance of the system is improved when the TFCsare recovered efficiently.

Accordingly, the prior art methods of handling the situation where theUE is in its maximum power state fall far short of acceptable systemperformance. It would be desirable to have an improved method ofexpeditiously reducing the set of TFCs for the duration when maximum UEpower condition is achieved, and expeditiously restoring the TFCs whenthe maximum UE power condition has passed.

SUMMARY

The present invention is system and method for enabling efficientreduction of TFCs in the TFCS to support a desired transmission, whileremaining within power and data requirements. In the event that the UEtransmission power requirements exceed the maximum or allowabletransmission power, the set of TFCs is reduced to only those acceptableTFCs that currently do not exceed the power limit. The UE will thenchose from among the acceptable reduced set of TFCs.

The invention also supports advanced determination of non-supportedTFCs. The TFCs that require transmission power greater then the maximumor allowed UE transmission power shall be determined continuously inevery TTI, not just in TTIs where the maximum power has been exceeded.The TFC selection process is adjusted to avoid selection of TFCs thatexceed transmission power capabilities in advance of transmission.

The present invention also enables the restoration of the TFCs in theTFCS when the maximum power condition no longer exists.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram for efficient removal of TFCs in accordancewith the present invention.

FIG. 2 is a flow diagram for restoration of TFCs in the TFCS.

FIG. 3 is a flow diagram for advance removal of TFCs in accordance withthe present invention.

FIGS. 4 and 5 are flow diagrams for two alternatives to determining TFCtransmit power requirements on a periodic basis.

FIG. 6 is a block diagram of the MAC entity and the physical entity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention will be described with reference to the drawingfigures wherein like numerals represent like elements throughout.

There are three basic aspects to dynamic link adaption in accordancewith the present invention. First, when a condition exists where the UEtransmission power requirement exceeds the maximum, or maximum allowed,power of the UE, the TFCs that require power in excess of the maximumpower limit are efficiently blocked. The MAC is informed, for subsequentTFC selection, of all TFCs that currently exceed this limit. Thereafter,only TFCs that do not require power in excess of the UE transmissionpower limit capability are available for selection.

Secondly, the present invention supports efficient recovery of TFCs inthe TFCS when the maximum power condition no longer exists.

Finally, the invention supports advance determination of non-supportedTFCs; i.e. those TFCs that require transmission power greater then themaximum or allowed UE transmission. These TFCs are determinedcontinuously and periodically, such as in every TTI, not just in TTIswhere the maximum power condition exists. Every TTI may or may notinclude TTIs where no data is transmitted. Since TFC requirements changeover time, this allows for advance determination of TFCs that will notbe supported.

It should be noted that although the present invention relates toremoval and restoration of TFCs, a minimum set of TFCs within theconfigured TFCS should always be available for transmission. Preferably,this minimum set is exempt from the TFC removal and restorationprocesses that will be described hereinafter.

The processes for TFC removal and restoration are performedperiodically. Although the period for these processes is describedhereinafter as being based on a TTI, it is also possible to performactions approximately every TTI, (i.e., more then once per TTI), orevery several TTIs. It should also be noted that every TTI may or maynot include TTIs where no data is transmitted.

Referring to FIG. 1, the procedure 10 for efficient removal of TFCs inaccordance with the present invention is shown. The procedure 10commences with selection of TFCs using the available set of TFCs (step16). The available set of TFCs is the initial full transport formatcombination set (TFCS) configured for the establishment of the CCTrCH.The selected TFC is sent to the physical entity 14 (step 18). Thephysical entity 14 determines the TFC transmission power requirement(step 22) and makes a determination of whether the required UE transmitpower for this TFC is over the maximum, or maximum allowable, UE power(step 24). If not, steps 16, 18, 22 and 24 are repeated until thetransmission power requirement for a TFC exceeds the maximum allowedpower. If for transmission of a TFC the UE power requirement is over themaximum allowed power, the physical entity 14 determines all TFCs withinthe TFCS that are in “excess power state” (step 25). The physical entity14 indicates the available or not-available (i.e. blocked) status of theTFCs to the MAC entity 12 (step 26). It should be noted that thephysical entity 14 can indicate the status of the available TFCs, thenot-available TFCs or both. The MAC entity 12 removes TFCs in the excesspower state as indicated by the physical layer entity 14 from theavailable set of TFCs (step 28). The procedure 10 is then repeated foreach TTI.

Although functionality is specifically identified as being performed inthe physical layer, it is also possible to perform some of these actionsin the MAC layer.

Referring to FIG. 2, the procedure 50 for restoration of TFCs in theexcess power state is shown. The MAC entity 12 selects a TFC using theavailable set of TFCs (step 52). The available set of TFCs is either theinitial full Transport Format Combination Set (TFCS) configured upon theestablishment of the CCTrCH, or a reduced available set of TFCs from theTFCS, which were previously indicated from the physical entity 14. Theselected TFC is sent to the physical entity 14 (step 53).

The physical entity 14 determines whether any TFCs are in the excesspower state (step 54). The determination is performed on a periodicbasis only for those TFCs within the configured TFCS that are in theexcess power state. This periodic basis may be, for example, every TTI.The physical entity 14 then determines whether any of the TFCs that werein the excess power state no longer exceed the maximum or maximumallowed power, and can be restored to the set of available TFCs (step55). The physical entity 14 then indicates restored TFCs to the MACentity 12 (step 56). If there is a change in available TFCs, (i.e. ifthe TFCs are unblocked), the MAC entity 12 updates its list of availableTFCs (step 58). Steps 52-58 are continuously repeated by the MAC andphysical layer entities 12, 14. This procedure 50 ensures that when TFCsare blocked, recovery of available TFCs are continuously determinedevery TTI, not just in TTIs where the maximum power has been exceeded.

The restoration of TFCs is much more efficient when unblocked TFCs areindicated on a periodic basis, rather than being determined by the UEcalculated transmitted power measurements on the transmitted signal,since the normal measurement reporting and processing mechanism is slow.This enables the UE to avoid reducing the transmitting rate to less thanthe data rate that is supported by the current channel conditions. TheUE can restore the desired TFCs based on the predicted transmitted powerrequirement prior to transmission, reducing the time required to restorethe TFCs by one or more TTIs.

Referring to FIG. 3, the procedure 150 advance removal of TFCs inaccordance with the present invention is shown. The procedure 150commences CCTrCH establishment and the configuration of the completeTFCS (step 151). A TFC is then selected from the available set of TFCs(step 152). The MAC entity 12 sends the selected TFC to the physicalentity 14 (step 154). The physical entity 14 continuously determines theavailable TFCs on a periodic basis (step 156), such as in every TTI asshown in FIG. 3. The ability to transmit all available TFCs is verified.A determination is made (step 157) as to whether any previouslyunblocked TFCs are now in the excess power state. If not, the procedure150 returns to step 152, to repeat the procedure 150. If so, the newTFCs now in the excess power state are indicated to the MAC entity 12(step 158). The MAC entity 12 updates the list of all available TFCs(step 160). It should be noted that steps 152, 154 and 160 performed bythe MAC entity 12 and steps 156, 157, 158 performed by the physicalentity 14 are continuously repeated, not necessarily in each TTI asrepresented in FIG. 3.

Since TFC transmission power requirements, which change over time, arechecked for restoration on a periodic basis, such as in each TTI, thismethod 150 allows for advance determination of TFCs that will not besupported. TFC power requirements are checked each TTI in step 156 todetermine if the maximum or maximum allowed power is exceeded. If thepower requirement cannot be satisfied for a TFC currently not blocked,the physical entity 14 indicates to the MAC entity 12 that this TFCshould be blocked (step 158). The TFC selection process is adjusted toavoid selection of TFCs that exceed transmission power capabilities inadvance of transmission of that TFC. Additionally, if the powerrequirement can be satisfied for a currently blocked TFC, the list ofallowable TFCs is continuously updated so that previously blocked TFCsmay be restored.

Advance determination may additionally employ logic that determineschange in radio propagation conditions over time. For example, thechange in pathloss from a received reference channel, or the change inreported uplink interference. These and other changes in radiopropagation conditions allow the UE to predict future transmission powerrequirements and block TFCs in advance of interference, pathloss orother conditions that would cause TFCs to enter an excess power state.

The result of the advance determination method 150 is the reduced lossof UL data and more efficient use of radio resources by the proper TFCselection for successful transmission. By blocking TFCs before TFCselection and transmission, user QoS is improved by reduced BLER, andphysical resources are better utilized by reducing the need forretransmissions. Since TrCH BLER is reduced, corresponding unnecessaryincreases in the UL SIR target is avoided, further increasing overallradio resource efficiency by reducing UL transmit power.

Although the methods 10, 50 and 150 to continuously update the availableTFCs provide for improved performance, the computational resourcesrequired to calculate the power requirements for every TFC every TTI isgreat. Accordingly, referring to FIGS. 4 and 5, two alternatives todetermining TFC transmit power requirements on a periodic, or TTI basis,are shown.

The method 70 of FIG. 4 commences with the MAC entity 12 using the setof TFCs which were determined upon CCTrCH establishment orreconfiguration (step 72). Upon CCTrCH establishment or reconfigurationthe configured TFCS is sorted by TFC according to transmission powerrequirements (step 74). Note that although indicated in the physicallayer 14, the sorted TFC list may be determined in either layer 2 orlayer 3 entities as well. In TDD systems, this list of TFCs may betimeslot specific, such as a sorted TFC list per timeslot. The physicalentity 14 periodically verifies the ability to transmit the TFC with thehighest transmission power requirement (step 76). A determination ismade as to whether the TFC can be transmitted (step 77). If this TFC canbe transmitted, a determination is made (step 79) as to whether therewere any blocked TFCs. If so, all the previously blocked TFCs are madeavailable (step 81) and the physical layer entity 14 goes to step 82 andindicates to the MAC entity 12 that all TFCs within the TFCS should beunblocked and are now available. If not, the procedure 70 returns tostep 76.

However, if it is determined (step 77) that the TFC with the highesttransmission power requirement cannot be transmitted or if the TFC withhighest transmit power requires a transmission power greater than themaximum allowed power, a procedure is implemented to approximate thestatus of each TFC in the sorted list (step 78). The specific process toefficiently determine which TFCs should be blocked is not central to thepresent invention, since there are numerous alternative options thatcould be utilized. In a first alternative of the present invention, forexample, since there is a sorted TFC list, the middle TFC within thelist is checked to see whether it can be transmitted. If it cannot betransmitted, the TFC in the middle of the lower half of the list ischecked to see if it can be transmitted. Likewise, if the TFC in themiddle of the list can be transmitted, the TFC in the middle of theupper half of the list is checked to see whether it can be transmitted.This process is repeated until the TFC with the highest powerrequirements that can be transmitted. Another alternative is to apply ahashing function to approximate the list index that exceeds the powercapability.

The physical entity 14 determines the TFCs that are not supported andpreviously blocked TFCs that are now supported (step 80), and indicatesthe updated available and blocked TFCs to the MAC entity (step 82).

An alternative to sending an updated complete list of unblocked TFCs, ora list of newly unblocked TFCs, from the physical entity 14 to the MACentity 12 is to transmit only an “index” to the sorted TFC list. Forexample, when the TFC list is sorted, entries above the index areblocked and entries below are unblocked. Transmission of the index willreduce the amount of control signaling required between the physicalentity 14 and the MAC entity 12.

A second alternative to sending an updated complete list of unblockedTFCs, or a list of newly unblocked TFCs, from the physical entity 14 tothe MAC entity 12 is to send a measured or calculated value from thephysical entity 14 to the MAC entity 12 (or any other layer 2 entity)which would allow the layer 2 entity to determine the new set ofavailable TFCs. It should be noted that many of the steps shown in FIG.4 as being performed by the physical entity 14 could also be performedby the MAC entity 12 such as steps 78 and 80.

Steps 76-82 are then repeated. Once the physical entity 14 transmits theupdated list, (or TFCS index or measured/calculated value) of allowableTFCs to the MAC entity 12, the MAC entity 12 updates the list ofavailable TFCs (step 84).

Referring to FIG. 5, a second alternative method 100 to periodicallydetermining TFC transmit power requirements is shown. The MAC entity 12initially uses the set of TFCs configured upon CCTrCH establishment orreconfiguration (step 102). Upon CCTrCH establishment orreconfiguration, each TFC is associated with a relative sensitivity.This can be done by the MAC entity 12, the physical entity 14 or anylayer 2 or layer 3 entities. This sensitivity can be an En/Norequirement under a certain propagation channel assumption, a maximumtolerable path loss under a propagation channel/transmit powerassumption or other method mapped onto integers 0-N. Additionally in TDDsystems, this relative sensitivity may be timeslot specific.

The MAC entity 12 forwards the selected TFC to the physical entity 14(step 104). The physical entity 14 transmits a TFC (step 106) anddetermines the margin relative to the maximum power (step 108). Thephysical entity 14 uses the margin to identify blocked and unblockedTFCs (step 110). It should be noted that this margin may be negative,which indicates a potential blocking, or positive, which indicates apotential recovery. These blocked and unblocked TFCs are then identifiedto the MAC entity (step 112). The physical entity 14 then repeats steps106-112 upon each TFC transmission. Having received the blocked andunblocked TFC indications from the physical entity 14, the MAC entity 12updates the list of blocked and unblocked TFCs (step 114). Steps 104 and114 are then repeated by the MAC entity 12.

Referring to FIG. 6, a block diagram of the MAC entity 12 and thephysical entity 14 is shown. The MAC entity 12 includes a TFC selectionprocessor 13, which selects the TFCs for transmission associated with aparticular CCTrCH supporting the desired TrCHs. Likewise, the physicalentity 14 has an allowed TFC processor 15 which determines blocked andunblocked TFCs and indicates the blocked and unblocked TFCs to the TFCselection processor 13. Although physical layer processing ispreferable, it is also possible to perform some of the aforementionedprocessing within the MAC layer or other layer 2 entities. In accordancewith the embodiments shown in FIGS. 4 and 5, the TFC processor 15 alsoperforms the sorting of the TFCs by UE transmission power requirements.The sorted list or the determination of the relative sensitivity canalso be determined in the TFC selection processor 13. Accordingly, thisprocessing may be performed in the physical layer, the MAC or otherlayer 2 entities, or even a layer 3 entity. The MAC entity 12 forwardsthe selected TFCs 17 (chosen from the available TFCs in the configuredTFCS) to the physical entity 14. In response, the physical entity 14indicates blocking and unblocking (removal and restoration) of TFCs 19.

It should be noted that although the methods 10, 50, 150 have beendescribed hereinbefore as separate procedures, it should clearly beunderstood by those of skill in the art that the methods may be combinedas desired for particular applications and processing may be performedat the same time. When combining logic in methods 10, 50 and 150, somechanges in the logic specified for each method are necessary forintegration of the methods to achieve proper operation. As such, whilethe present invention has been described in terms of the preferredembodiments, other variations, which are within the scope of theinvention, as outlined in the claims below will be apparent to thoseskilled in the art

What is claimed is:
 1. A method for selecting a transport formatcombination (TFC), implemented by a user equipment, the methodcomprising: receiving configuration of a plurality of TFCs to use forTFC selection, wherein the TFCs of the plurality of TFCs have an order;determining TFCs to block from TFC selection from the plurality of TFCs,wherein the TFCs to block are based at least on a maximum allowedtransmit power; and selecting a TFC for transmission of uplink data,wherein the selecting the TFC is based on the TFC order and wherein theselected TFC is a TFC that is not blocked from TFC selection.
 2. Themethod of claim 1, wherein the determining TFCs to block from TFCselection takes places at least once every transmission time interval.3. The method of claim 1, wherein the configuration of the plurality ofTFCs is an initial configuration.
 4. The method of claim 1, wherein theconfiguration of the plurality of TFCs is a reconfiguration.
 5. Themethod of claim 1, wherein the TFC order is based on a transmissionpower requirement.
 6. The method of claim 1, wherein the selected TFC isderived from a margin.
 7. The method of claim 6, wherein the margin isderived from the maximum allowed transmit power.
 8. A user equipmentcomprising: circuitry configured to receive configuration of a pluralityof transport format combinations (TFCs) to use for transport formatcombination (TFC) selection, wherein the TFCs of the plurality of TFCshave an order; circuitry configured to determine TFCs to block from TFCselection from the plurality of TFCs, wherein the TFCs to block arebased at least on a maximum allowed transmit power; and circuitryconfigured to select a TFC for transmission of uplink data, wherein theselected TFC is based on the TFC order and wherein the selected TFC is aTFC that is not blocked from TFC selection.
 9. The user equipment ofclaim 8, wherein the circuitry configured to determine TFCs to blockfrom TFC selection is configured to take places at least once everytransmission time interval.
 10. The user equipment of claim 8, whereinthe configuration of a plurality of TFCs is an initial configuration.11. The user equipment of claim 8, wherein the configuration of aplurality of TFCs is a reconfiguration.
 12. The user equipment of claim8, wherein the TFC order is based on a transmission power requirement.13. The user equipment of claim 8, wherein the selected TFC is derivedfrom a margin.
 14. The user equipment of claim 13, wherein the margin isderived from the maximum allowed transmit power.